When I set up my Web UI behind the Cloudflared tunnel, I get

403 Forbidden

Your IP is not whitelisted to access this service.

When I try to log into the panel.

Make sure you follow the instructions correctly outlined in this guide:

Also, check the installation and troubleshooting guides:

If you're still stuck, please drop us a ticket.

I had a similar problem, had to add ::1 to the whitelist, give that a try!